TaskAttemptID represents the immutable and unique identifier for
a task attempt. Each task attempt is one particular instance of a Map or
Reduce Task identified by its TaskID.
TaskAttemptID consists of 2 parts. First part is the
TaskID, that this TaskAttemptID belongs to.
Second part is the task attempt number.
An example TaskAttemptID is :
attempt_200707121733_0003_m_000005_0 , which represents the
zeroth task attempt for the fifth map task in the third job
running at the jobtracker started at 200707121733.

Applications should never construct or parse TaskAttemptID strings
, but rather use appropriate constructors or forName(String)
method.